Lots of good info there - Thanks Hack.
I have confirmed that the restrictor plate is there.
I ordered the 180° Thermostat from Mustang Unlimited which looks like this: (which seems to be the popular choice in the linked threads)
The 192° one they offer looks completely different (and is half the price):
While I was there I also ordered a new Thermostat housing since the old one was just too nasty to be worth playing with. I got this one:
Now that I look at that Mustang Unlimited page again, I probably should have gotten the chrome (Scott Drake) one for the same price (though it would look kinda stupid on my - much less than impressive - no chrome anywhere - engine). (Plus I've had mixed experiences with Scott Drake products) Here's a pic anyway:
Though I assume it will be fairly obvious, my shop manual doesn't show the correct thermostat insertion direction nor order of assembly. My guess is:
1. Large round portion of thermostat down towards restrictor plate
2. then gasket over that (with sealant - RTV or Gasket Ahdesive - on both sides of gasket)
3. then Thermostat housing - torq bolts to 12 ft. lbs.